......
import org.eclipse.ui.editors.text.TextEditor;
import javax.swing.event.DocumentEvent;
import javax.swing.event.DocumentListener;
......

public class test(){
private TextEditor editor;
......

editor.getDocumentProvider().getDocument(editor.getEditorInput())
        .addDocumentListener(new DocumentListener(){
    @Override
    public void changedUpdate(DocumentEvent arg0) {
    // TODO Auto-generated method stub                                
    }
    @Override
    public void insertUpdate(DocumentEvent arg0) {
    // TODO Auto-generated method stub                                
    }
    @Override
    public void removeUpdate(DocumentEvent arg0) {
    // TODO Auto-generated method stub                                
    }                             
});
.......
}